Cartridges and systems for membrane-based therapies

ABSTRACT

A cartridge is provided for dialysis or other blood processing therapy. In the cartridge, fibers may be substantially uniformly distributed near a midplane, but near an end, in the inter fiber space, there may be void flow channels, which may cause fluid flow in the inter fiber space to transition within a short region to uniform flow with minimal stagnation zones. Void flow channels may be be radially oriented, introducing fluid from the outer circumference, or axially oriented, introducing fluid along the axial direction through passageways through the potting material. The fluid flow in the inter fiber space may be perpendicular to the fibers, or radial with respect to a cartridge longitudinal axis. The cartridge may have blood flow in the inter fiber space, and flow of dialysate or ultrafiltrate in the lumens of the fibers, or the opposite situation.

CROSS-REFERENCE TO RELATED APPLICATION

The present application includes the disclosures of U.S. provisionalSer. No. 62/222,901 that was filed with the United States Patent andTrademark Office on Sep. 24, 2015 and U.S. provisional Ser. No.62/238,214 that was filed on Oct. 7, 2015. A priority right is claimedto U.S. provisional Ser. Nos. 62/222,901 and 62/238,214 to the extentappropriate. The complete disclosures of U.S. provisional Ser. Nos.62/222,901 and 62/238,214 are incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the invention pertain to hemodialysis and relatedtherapies and processes, and pertain to cartridges and filters toperform such therapies and processes.

BACKGROUND OF THE INVENTION

Hemodialysis and related processes are used to treat large numbers ofpatients suffering from renal failure and other conditions, includingboth acute and chronic conditions. However, improvement is still neededin, among other features, the length of time that an individual filtercartridge can be used without suffering from clot formation and filterclogging. There also is a need, for whatever fluid is flowing in theinter fiber space, for more uniform flow distribution in the inter fiberspace, with stagnation regions being either non-existent or as small aspossible.

SUMMARY OF THE INVENTION

In an embodiment of the invention, there may be provided: a cartridgefor processing a fluid, the cartridge comprising: a housing that isgenerally tubular, having a housing wall and having a midplane; aplurality of fibers, at least some of the fibers being hollow and havingporous walls or a semipermeable membrane, at least portions of thefibers being contained within the housing, the fibers being potted neartheir ends in a potting material, wherein the plurality of fibers arearranged as a fiber bundle of fibers that are generally parallel to eachother at least at the midplane, the fibers in the fiber bundle having anaverage fiber-centerline-to-fiber-centerline spacing at the midplane,wherein, adjacent to the potting material, the fiber region contains atleast one void flow channel that is substantially open and has atransverse dimension that is at least 3 times the averagefiber-centerline-to-fiber-centerline spacing at a midplane of thecartridge, wherein the void flow channel adjoins an outer circumferenceof the fiber bundle and extends inward to a radially more inwardlocation.

It is possible that the pattern of the void flow channel can be observedon the cut and polished end of the potting material. The pattern of thevoid flow channel can be observed on the surface of the potting thatfaces the inter fiber space. The void flow channels may comprise twodifferent sizes of void flow channels, which may alternate with eachother proceeding around the circumference of the fiber bundle. The voidflow channels may be distributed at equiangular locations around theperimeter of the fiber bundle. The cartridge can include fanning of thefibers near the end of the cartridge, such as by virtue of a taperedinternal surface of the housing. The geometry of the cartridge may besuch that there is a midplane porosity fraction, and the geometricfanning factor and the porosity fraction increase upon getting closer tothe end of the cartridge. The housing internal taper that helps toproduce fanning may begin closer to the midplane of the cartridge thanthe potting tool fingers are located during manufacture. In thissituation, the porosity of the fiber bundle may be calculated as theporosity of the fiber bundle excluding the void flow channel(s), i.e., avoid-adjusted porosity. The void-adjusted porosity may increasecontinuously toward the end of the cartridge. The void-adjusted porositymay be larger immediately next to the potting material than it isanywhere else between the midplane and that end.

In an embodiment of the invention, there may be provided: a cartridgefor processing a fluid, the cartridge comprising: a housing that isgenerally tubular, having a housing wall; a plurality of fibers, atleast some of the fibers being hollow and having porous walls or asemipermeable membrane, at least portions of the fibers being containedwithin the housing, wherein the plurality of fibers are arranged as abundle of fibers that are generally parallel to each other at acartridge midplane, the fibers in the bundle having an averagefiber-centerline-to-fiber-centerline spacing at the cartridge midplane,wherein, near an end of the cartridge, the fiber region contains atleast one void flow channel that is substantially open and has atransverse dimension that is at least 3 times the averagefiber-centerline-to-fiber-centerline spacing at a midplane of thecartridge, wherein the cartridge has a potted region that adjoins endsof the fibers, and a supply passageway extends through the potted regionfrom an outward-facing surface of the potted region to an opposedinward-facing surface of the potted region and is in fluid communicationwith the void flow channel.

In an embodiment of the invention, there may be provided: a cartridgefor processing a fluid, the cartridge comprising: a housing, having ahousing wall; a plurality of fibers, at least some of the fibers beinghollow and having porous walls or a semipermeable membrane, at leastportions of the fibers being contained within the housing, wherein theplurality of fibers are arranged as a bundle of fibers that aregenerally parallel to each other, wherein blood flows over the exteriorsurfaces of the fibers in a direction substantially perpendicular to thefiber axis, wherein fluid in an inter fiber space flows perpendicular tothe fibers and generally parallel to a surface of the housing.

In an embodiment of the invention, there may be provided: a cartridgefor processing a fluid, the cartridge comprising: a housing, having ahousing wall; a plurality of fibers, at least some of the fibers beinghollow and having porous walls or a semipermeable membrane, at leastportions of the fibers being contained within the housing, wherein theplurality of fibers are arranged as a bundle of fibers that aregenerally parallel to each other, wherein fluid in the inter fiber spaceflows perpendicular to the fibers and generally radially with respect toa longitudinal axis of the cartridge.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

Embodiments of the invention are further described but are in no waylimited by the following illustrations.

FIG. 1 is an oblique cut away view showing the construction and use of atypical filter cartridge used in medical procedures.

FIG. 2 is an oblique cutaway view of the inlet end of the filtercartridge of FIG. 1, illustrating typical clotting.

FIG. 3 is an oblique illustrative view of three fibers of the filtercartridge in FIG. 2, showing the effect of clotting.

FIG. 4 is an oblique cutaway view showing an improved use of a filtercartridge for dialysis or ultrafiltration.

FIG. 5 is an oblique illustrative view of three fibers of the filtercartridge in FIG. 4, showing the effect of clotting.

FIG. 6A is a partial cross-sectional view of the filter cartridge ofFIG. 4, illustrating the blood flow into the fiber bundle, for acartridge that does not have an orbital distributor.

FIG. 6B is a cross-sectional view of a filter cartridge showing flowpatterns in a situation where the cartridge contains an orbitaldistributor.

FIG. 7A is an oblique partial cross-sectional view of a housing of afirst embodiment of the invention, having a plurality of radial inletports, and having an interior that is tapered near the end while havinga generally cylindrical tube exterior.

FIG. 7B is a similar view of a housing in which both the outside of thetube and the inside of the tube are tapered.

FIG. 8 is an oblique partial cross-sectional view of the housing of FIG.7A, showing the placement of the fiber bundle.

FIG. 9 is an oblique partial view of a housing, with fiber bundle inplace, being introduced to potting tooling.

FIG. 10 is an oblique partial cross-sectional view of a housing, withfiber bundle in place, enclosed for potting.

FIG. 11A is an oblique partial cross-sectional view of the filtercartridge and potting tool of FIG. 10, after a potting material has beeninjected and cured.

FIG. 11B is another possible tooling arrangement, in which there isprovided a potting cap that is separate from the potting tool fingers.

FIG. 12A is an oblique partial view of a potted filter assemblage, withthe filter assemblage having been cut and polished in a first location,showing an outwardly-facing surface.

FIG. 12B is a similar view of the potted filter assemblage having beencut and polished in a second, slightly different location.

FIG. 12 C is a view in the direction indicated in FIG. 12A, showing voidflow channels and distribution of fibers on an inwardly-facing surfaceof the barrier.

FIG. 12D shows an embodiment in which the void flow channels are of twodifferent sizes, alternating in position around the circumference of thefiber bundle. In FIG. 12D, eight such voids are shown.

FIG. 12E shows an embodiment similar to FIG. 12D, in which twelve suchvoid flow channels are shown.

FIG. 12F shows yet another possible arrangement of void flow channels,in which the void flow channels are curved.

FIG. 12G is an illustration showing how the local fiber porosity couldvary as a function of position along the longitudinal axis of thecartridge, taking into account both fanning of fibers and fiberrearrangement caused by the potting tool fingers.

FIG. 13 is an oblique partial cross-sectional view of a completed filtercartridge of the first embodiment.

FIG. 14, for a second embodiment, is an oblique partial cross-sectionalview of a housing containing a fiber bundle.

FIG. 15 is a front partial cross-sectional view of the housing of FIG.14, with a potting cap applied.

FIG. 16 is a front partial cross-sectional view of the housing andpotting cap of FIG. 15, with potting material injected.

FIG. 17A is an oblique partial cross-sectional view of the filterassemblage of FIG. 16, with the potting cap removed, and the excesspotting material and the fiber bundle cut back.

FIG. 17B is an illustration showing how the local fiber porosity couldvary as a function of position along the longitudinal axis of thecartridge, taking into account both fanning of fibers and fiberrearrangement caused by the potting tool fingers.

FIG. 18 is a partial front cross-sectional view of the completed filterof the second embodiment.

FIG. 19 is an oblique view of a filter base for a flat cross-flow filterof a third embodiment of the invention.

FIG. 20 is an oblique partial cross-sectional view of the filter base ofFIG. 19, with a screen installed.

FIG. 21 is an oblique view of the filter base of FIG. 19, with screensand fiber bundle installed.

FIG. 22 is an oblique view of the filter assemblage of FIG. 21, withcover installed.

FIG. 23 is an oblique view of the filter assemblage of FIG. 22, afterpotting.

FIG. 24 is an oblique cross-sectional view of the filter assemblage ofFIG. 23, with potting and fiber ends trimmed, illustrated with onedialysate cap in place.

FIG. 25 is an oblique view of a filter screen used in the constructionof a fourth embodiment of a filter cartridge for dialysis orultrafiltration.

FIG. 26 is an oblique view of the filter screen of FIG. 25, with a fiberbundle inserted therein.

FIG. 27 is a front cross-sectional view of the filter screen and fiberbundle of FIG. 26 inserted into a housing.

FIG. 28 is a top view of the filter screen, fiber bundle, and housing ofFIG. 27.

FIG. 29 is a broken front cross-sectional view of the filter assemblageof FIG. 28, with first and second potting tools.

FIG. 30 is a broken front cross-sectional view of the filter assemblageand potting tools of FIG. 29, after potting material injection.

FIG. 31 is a broken oblique cross-sectional view of the filterassemblage of FIG. 28, after trimming.

FIG. 32 is a broken front cross-sectional view of the completed fourthembodiment of the filter cartridge.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, FIG. 1 illustrates a Prior Art cartridge thatmay be used to treat patients requiring hemodialysis or other relatedtherapies. Such cartridges generally comprise a fiber bundle 2positioned within a housing 1. Fiber bundle 2 comprises a plurality ofhollow fibers, the ends of which are embedded in a potting material 3,commonly a thermosetting material, such as urethane. The pottingmaterial 3 is generally introduced as a liquid, and is cured toencapsulate the ends of all fibers. After curing, the potting resin 3and the ends of fiber bundle 2 are cut away, to re-expose the lumens ofthe fibers.

In conventional forms of hemodialysis, a patient's blood is introducedto inlet header 4, flows through the lumens of the fibers of fiberbundle 2, and exits through an outlet header at the other end of thecartridge. A dialysate solution is introduced through inlet port 7,flows over the exterior surface of the fibers in fiber bundle 2, andexits through outlet port 6.

In some dialysis procedures, bodily waste products in the blood maydiffuse or be transported by convection through the fiber walls or maypass through a plurality of microscopic pores in the fiber walls, orboth. The removed waste products are carried away by the dialysate flow.In the management of hypervolemia, membrane hollow fibers are used toremove excess fluid from the blood by ultrafiltration. In relatedtreatment modalities, a dialysate-like fluid may be introduced intoinlet port 7, to carry excess patient fluids away through outlet port 7.Alternatively, inlet port 7 may be plugged, and outlet port 6 used toremove the excess patient fluids, such as in Slow ContinuousUltraFiltration (SCUF) therapy.

FIG. 2, which is also Prior Art, depicts the inlet header 4 portion ofthe filter of FIG. 1, and illustrates the possible formation of bloodclots 8, which may form and then occlude the lumens of fibers of fiberbundle 2, decreasing the effectiveness of the filter cartridge, orrendering it unusable after substantial clogging of the fibers in thebundle. FIG. 3, which is also Prior Art, illustrates three fibers of atypical fiber bundle 2 of the filter of FIG. 1 and of FIG. 2. Hollowfibers of the type used in dialysis and ultrafiltration commonly may be150 to 300 microns in outside diameter, with lumens of 100 to 250microns diameter. Even small blood clots 8 may partially or fullyocclude the lumen of a fiber, thus rendering the entire length of thatfiber less effective, or non-effective. As illustrated, some of theblood flow 28 is blocked by such clots in the lumens of fibers.

Such a filter cartridge 30 for dialysis or ultrafiltration is typicallyconstructed by placing a fiber bundle 32 in a housing 31, and immersingthe ends in a potting material 33, such that the ends of the fibers offiber bundle 32 are encapsulated in the potting material 33, and thencuring potting material 33. After curing, the potting material 33 andthe ends of fiber bundle 32 are cut away, to re-expose the lumens of thefibers. Within fiber bundle 32, there exists some space between fibers,designated the inter fiber space.

As shown in FIG. 4, in an embodiment of the invention, filter cartridge30 may be used such that a patient's blood may be introduced to theinter fiber space of the cartridge through blood inlet 36, and may flowpast the exterior surfaces of the fibers of fiber bundle 32, exitingthrough blood outlet 37. This configuration, which differs from commonpractice, may be termed Outside-In Flow Filtration. If dialysis is beingperformed, dialysate may be introduced through inlet port 35, and mayflow through the lumens of the fibers of fiber bundle 32, and may exitthrough outlet port 34. In some treatments requiring additionalultrafiltration, a dialysate-like fluid may be introduced into inletport 35, to carry excess patient fluids away through outlet port 34.Alternatively, inlet port 35 may be closed off, and outlet port 34 maybe used to remove the excess patient fluids by means of anultrafiltration process.

In FIG. 5, the blood flow 42 and dialysate flow 43 are illustrated forthe structure of Outside-in Flow Filtration cartridge 30 shown in FIG.4. Assuming that blood clots 44 form, they are positioned on theexterior of fibers 41, in the interstitial space between the fibers.Since the interstitial space between fibers 41 is all interconnected,blood can easily detour around clots, and continue along the fiberbundle 32. Thus blood clots 44 render only a very small portion of thelength of any fiber ineffective, and there still remain some fluid flowpaths open in the inter fiber space.

While the flow regime illustrated in FIG. 5 has advantages over theconventional flow regime of the conventional cartridge of FIG. 1, therestill remain some inefficiencies resulting from the details by which theblood is admitted into fiber bundle 32 through blood inlet 36.

FIG. 6A illustrates one such problem. For this relatively simplegeometry as illustrated, blood flow 42 from a patient enters the filtercartridge through blood inlet 36, and flows into the interstitial spacebetween filter fibers 46, somewhat impeded by the filter fibers that arelocated directly adjacent to blood inlet 36. Within a portion of thelength of filter fibers 46, approximately up to line T-T, the blood flow42 transitions from the lateral or radial flow through blood inlet 36,to an axial flow along the longitudinal direction of filter fibers 46.Blood flow in the area labeled S may have a relatively small velocity,or may be stagnant, and thus the portions of filter fibers 46 withinarea S may operate at a lower efficiency for filtration or dialysis. Lowflow velocity and stagnation also increase the propensity for the bloodto form clots in those locations or may lead to sequestration orretention of leukocytes. These events may lead to adverse consequencesincluding complete clogging of the filter. What is illustrated in FIG.6A is a relatively simple design of dialyzer, which does not include anorbital distributor for the flow in the inter fiber space. In some otherdesigns of dialyzers, there may be provided an orbital distributor,which conducts fluid around substantially the entire perimeter of thefiber bundle so that fluid can enter or exit the fiber bundlesubstantially all around the perimeter of the fiber bundle. This isillustrated in FIG. 6B. In a dialyzer cartridge that contains an orbitaldistributor, there may be a flow stagnation region having a slightlydifferent location and shape from what is illustrated in FIG. 6A. Forthis situation, a flow stagnation region may exist near the end of theinter fiber space, on or near the axis of the fiber bundle. This isillustrated as Region S in FIG. 6B.

In embodiments of the invention, it is desired to have flow in the interfiber space be as uniform as possible for as great a length as possible,and it is desired that flow stagnation regions be either eliminated ormade as small as possible. If the fluid flowing in the inter fiber spaceis blood, this strategy can be beneficial in terms of reducing clotformation and other undesirable effects. If the fluid flowing in theinter fiber space is dialysate or a similar liquid, this strategy can bebeneficial in terms of improving the efficiency and clearance of thedialyzer. It is possible that the need for flow uniformity and lack ofstagnation regions may be more stringent when the fluid in the interfiber space is blood (as opposed to dialysate), but such importance canbe determined according to the details of a particular situation.

It is believed, although it is not wished to be limited to thisexplanation, that the following guidelines help to achieve and maintainuniformity of distribution of spacing of fibers within the housing (withthe exception of the spacing of fibers at the void flow channelsdescribed herein that may be intentionally created near the ends of thecartridge): the use of fibers that are wavy; and a porosity of the fiberbundle ranging from 70% to 40% (corresponding to a packing fractionranging from 30% to 60%), more particularly a porosity fraction that isbetween 50% and 62%. For use in situations that provide blood flowing inthe inter fiber space, the fibers may have exterior surfaces that aresmooth and hemocompatible.

In many situations, cartridges of the types described herein have twoends that are mirror images of each other or are symmetric about a planethat is perpendicular to the longitudinal axis of the filter. Such planemay be located midway between the ends of the cartridge and may bereferred to as the midplane of the cartridge. However, embodiments arealso possible in which the ends of the cartridge differ from each otherin some respect. For example, such differences could be in the presenceor absence of a distributor; design of the distributor at respectiveends of the cartridge; presence or absence of fanning of fibers; fanningangle, area ratio or other details of fanning of fibers at respectiveends; and presence or absence or design details of void flow channels atrespective ends of the cartridge. At a middle or midplane (midwaybetween the ends of the hollow fibers), the fibers may be substantiallyuniformly distributed, having an average spacing between the fibers,which can be described as an averagefiber-centerline-to-fiber-centerline distance.

Various embodiments of the invention may be provided to overcome orimprove upon less-than-ideal flow situations such as were illustrated inFIGS. 6A and 6B.

Embodiment 1

A first embodiment of the invention is described in FIGS. 7A through 13.The completed cartridge is shown in FIG. 13, and it may be constructedin accordance with the steps shown in FIGS. 7A through 12G. In thisfirst embodiment, void flow channels are provided extending into thefiber bundle from the outside circumference of the fiber bundle.

The embodiments and construction steps described below are described inreference to a first end of such a cartridge, but it is intended thatidentical steps could also be performed in the manufacturing of thesecond end of the cartridge. It is also contemplated, alternatively,that the two ends of the cartridge could differ from each other in someway, as discussed elsewhere herein.

In embodiments of the invention, there may be provided a housing, and aplurality of fibers, at least some of the fibers being hollow and havingporous walls or being semipermeable membranes, at least portions of thefibers being contained within the housing. The fibers may have anaverage fiber-to-fiber spacing at a mid-region of the cartridge, withmid-region referring to midway between the two ends of the cartridgewith respect to a longitudinal direction of the cartridge. Similarly,midplane can be a plane cutting through the cartridge, perpendicular tothe longitudinal axis of the cartridge, midway between the two ends ofthe cartridge. The term fiber-to-fiber spacing may be understood torefer to distance between centerlines of nearest-neighbor fibers.

In some embodiments of the invention, some local void flow channels areprovided in the fiber bundle near an end of the fiber bundle. The voidflow channels can be considered to be regions having no fibers, suchthat the void flow channel has a transverse dimension that is at least 3times or at least 5 times an averagefiber-centerline-to-fiber-centerline spacing at the midplane of thecartridge. Transverse can mean generally perpendicular to the principalor lengthwise direction of the void flow channel, and also generallyperpendicular to the longitudinal direction of the cartridge. The voidflow channels can allow fluid in the void flow channel to flow intointerior portions of the fiber bundle more easily than would be true ifthe void flow channel were absent and the flow had to cross or pass by anumber of typically-spaced fibers to reach interior portions of thefiber bundle. With respect to the longitudinal direction of thecartridge, in this embodiment, the void flow channels may occupy alimited region near an end of the cartridge. It is envisioned that for asubstantial fraction of the length of the cartridge especially themiddle of the cartridge, the fiber bundle would contain fibers that aresubstantially uniformly spaced within the housing. The presence of thevoid flow channels near an end of the fiber bundle can allow theentering fluid flow to enter more easily and directly into the interiorof the fiber bundle, and to do so within a relatively small distancealong the longitudinal direction of the cartridge. It is expected thatas entering fluid flow approaches the fiber bundle at the outercircumference of the fiber bundle, depending on the design of theorbital distributor, a portion of the flow may enter the fiber bundledirectly if the design of the orbital distributor permits this, and asignificant portion of the flow may enter the void flow channel(s) andmay flow inward into the fiber bundle along the principal direction ofthe void flow channel(s), with the flow gradually exiting from the voidflow channel through the boundaries of the void flow channel into thefiber bundle. Thus, flow can easily access portions of the fiber bundlethat are well inside the fiber bundle, without having to flow past oraround a large number of fibers to get deep inside the fiber bundle. Ifa similar geometry is provided at the discharge end of the cartridge, itcan be expected that there would exist similar flow patterns at thedischarge end of the cartridge, but the flow patterns would beoppositely directed in the sense of exiting rather than entering. It mayalso be desirable that the exit distributor be of the orbital type suchthat it will function as a trap to capture any loose clots that maybecome loose during treatment, and thus prevents their travel with bloodstream to the patient's body.

It is expected that, as a result of such design features, the flowtransitions into a uniform axial flow along the longitudinal directionof the cartridge, within a transition region that occupies only arelatively short length along the longitudinal direction of thecartridge. This represents an improvement over, for example, thesituation illustrated in FIGS. 6A and 6B.

Referring now to FIGS. 7A and 7B, a housing 60 has a tube end portion 62having an interior that is tapered near the end such that the innerdiameter of the tube increases toward tube end 66. A plurality of radialports 64 are provided in tube end portion 62 of the housing 60, inproximity to tube end 66. In FIG. 7A, the outside of the tube isillustrated as being generally cylindrical even while the inside of thetube is tapered near the end of the tube. Accordingly, it is illustratedin FIG. 7A that the tube has an outside diameter. In FIG. 7B, the insideof the tube is again internally tapered near the end of the tube, and inFIG. 7B the outside of the tube is tapered near the end of the tube.Accordingly, it is illustrated in FIG. 7B that there is a taper anglealpha describing the taper of the outside of the tube with respect to alongitudinal centerline of the tube. Other geometries near the end ofthe tube are also possible. Furthermore, with regard to both FIG. 7A andFIG. 7B, it is possible that an additional piece may at some point bejoined to the outside of the tube to provide an orbital distributor orother feature. Also, although the tube is shown as being generallyaxisym metric, other shapes are also possible for one skilled in theart, such as oval, rectangular, etc.

In this first embodiment (and later the second embodiment as well), itwould be possible to manufacture the housing initially in two parts,with the two parts eventually being joined to each other. For example,the joint could be at or near the midplane of the cartridge. Such atechnique would, for example, allow the formation of the internal tapernear both ends of the housing. Alternatively, it may be possible tomanufacture the housing as a single piece such as by extrusion, and forman internal taper if desired by appropriate means. In any instance, itis further possible for another piece such as an orbital distributor tobe joined to the tubular housing at some stage of manufacture.

Referring now to FIG. 8, a fiber bundle 68 has been placed into housing60 of FIG. 7A. (Although this is illustrated using the housing of FIG.7A, these steps could similarly be performed for the housing of FIG. 7Bif that is the type of housing used.) Preferably, at this stage, fiberends 70 protrude slightly beyond tube end 66.

It is possible that at this stage of manufacturing, prior to potting,the ends of the hollow fibers may be closed or sealed. Such a step wouldavoid intrusion of potting resin into the lumens of the fibers duringthe potting process. It is possible to seal the fiber ends using anyform of application of heat. For example, a non-contact heat source suchas radiant heating could be used. It is further possible that a lasercould be used both for cutting the fibers to length and for sealing theends of the fibers in a single operation, or alternatively, cuttingcould be a separate operation and sealing could be a separate operation.Either or both steps could be performed by a laser. Alternatively, stillother manufacturing processes are also possible, such as multiplepotting steps involving a first potting step to seal the fiber ends anda second potting process to cast the potting that will remain in thefinished product. The sealing step could be performed after the fibersare in the housing, although if desired it would be possible to performsuch step before the fibers are introduced into the housing.

As illustrated in FIG. 9, into the filter assemblage of FIG. 8 areintroduced a plurality of potting tool segments 72, each segmentcomprising a wedge shaped potting tool end segment 74, a potting toolcylinder segment 76, and a potting tool finger 78. (For clarity ofillustration, the potting tool segments 72 are shown for onlyapproximately half of the circumference of the fiber bundle.) Eachpotting tool finger 78 may have a potting tool finger tip 80.

The potting tool fingers 78 are illustrated as being solid entities.First of all, the potting tool finger 78 may have a surface that issmooth and may have edges that are rounded or tapered as appropriate forgently displacing fibers as the potting tool finger is advanced into thefiber bundle. However, in addition to what is illustrated, there alsoare other possible design features that could be used toward a goal ofminimizing possible damage to the fibers. For example, it iscontemplated that the potting tool finger could deliver flowing gas tothe fiber bundle as the potting tool fingers are advancing into thefiber bundle to create the pattern of void flow channels. The gas couldbe delivered through small holes in the surface of the potting toolfingers. If this is done, the holes could be provided in the pottingtool fingers in the region of the eventual inter fiber space, and not inthe region of the potting tool that will be exposed to potting material.Alternatively, or in addition, it is possible that as the potting toolfingers are advancing into the fiber bundle, gas could be caused to flowin the inter fiber space along the axial direction of the fiber bundle.Another possibility is that the potting tool fingers could be made ofmultiple parts that separate from each other, such as by a hinge or bybending, after or while the potting tool fingers 78 are advanced intothe fiber bundle. Not only can such process steps and features avoiddamaging individual fibers, but they may present another advantage also.They may encourage the fibers to become uniformly spaced in theremaining space and shape of the fiber bundle, as opposed to having a“bunching-up” featuring an increased local packing density near thepotting tool finger.

It is shown in FIG. 9 that proceeding in a radially inward direction,the potting tool finger 78 may be tapered to a thin edge that is roundedor radiused at its radially innermost tip. As illustrated, the pottingtool finger 78 may extend radially inward more than half of a radialdimension of the fiber bundle but might end before it reaches a centrallongitudinal axis of the fiber bundle. Similarly, the void flow channels82, which result from the positioning of the potting tool fingers andremain after potting, similarly may extend radially inward more thanhalf of a radial dimension of the fiber bundle but might not extendentirely to a central longitudinal axis of the fiber bundle.

Each potting tool finger 78 also may have a taper with respect to anaxial direction. As illustrated, the potting tool finger may taper so asto become thinner and eventually vanish in the direction toward themidplane or mid-region of the cartridge. The resulting void flow channel82 created by the potting tool finger may have a similar taperingproperty and shape. Any edges of the potting tool fingers 78 may becontoured or radiused as desired, especially if they are located near ormay contact fibers.

As illustrated, the number of potting tool segments and fingers is six.However, it can be appreciated that other numbers of potting toolsegments and fingers are also possible. As illustrated, all of thesefeatures are distributed at equal angular intervals around thecircumference of the fiber bundle. Such symmetry may be advantageous inachieving a uniform and rapid transition to a uniform axial flow wherethe axial component of the velocity vector is more than 70% orpreferably more than 90% of the overall velocity vector, and thedistribution of flow in the fiber bundle is substantially uniform.However, it can be understood that other patterns of positions of thepotting tool fingers are also possible and symmetry is not essential.

The potting tool segments 72 shown in FIG. 9 are arranged to moveradially inward so that when they meet they enclose the end of housing60 as shown in FIG. 10. In FIG. 10, potting tool segments 72 have beenmoved inward radially to enclose the end of housing 60. (Again, forclarity of illustration, the potting tool segments 72 are shown for onlyapproximately half of the circumference of the fiber bundle.) Pottingtool end segments 74 have come together to form an enclosed space ashort distance beyond the fiber ends 70 of fiber bundle 68. It can beconsidered that potting tool end segments 74 form a potting cap thatcontains and limits the flow of the resin during the potting process.The space inside the potting cap can be accessed through access port87A. As illustrated in FIG. 10, potting tool fingers 78 have passedthrough radial ports 64 of housing 60, and into fiber bundle 68. Radialports 64 may be dimensioned so as to allow potting tool fingers 78 topass through them. The shape of radial ports 64 may be generallycomplementary to the shape of potting tool fingers 78 where potting toolfingers 78 pass through radial ports 64. Radial ports 64 may, forexample, be rounded rectangles. Potting tool fingers 78 may locallydisplace fibers in fiber bundle 68 in a generally circumferentialdirection. Stiffness of the displaced fibers in fiber bundle 68 mayresult in the formation of separation patterns or void flow channels 82in fiber bundle 68 that extend or continue for some distance immediatelyabove and/or below potting tool fingers 78.

FIG. 11A shows the filter and potting tooling illustrated in FIG. 10,after injection and curing of a potting material 84. Potting materialsare typically thermosetting materials which are injected into thepotting tooling as a viscous liquid. Chemical reactions within thematerial then cause it to cross link and set into a relatively hardsolid material. As illustrated in FIG. 11, potting material 84 may beinjected until it fills a fiber void flow channel 82 that is near theend of the cartridge, fiber bundle interstitial space, and anyadditional space within potting tool segments 72, as far as a leveldepicted by line L-L. So, portions of the potting tool may serve as thepotting cap that limits the spread of the resin during potting. Theviscosity of the potting material 84, as it is injected, may be chosensuch that the uncured potting material surrounds and conforms to theexteriors of the fibers but possibly does not enter the open fiberlumens to any great extent if the fiber lumens are open at their ends.It is furthermore possible that the ends of the fibers may have beensealed or closed prior to the potting operation.

Finger 78 may be tapered in such a way as to aid in removal of finger 78from potting material after potting material has been cured, i.e.,finger 78 may have a draft angle to aid in retraction of finger 78 fromthe potting material. The potting tool fingers can be made of a materialthat the potting material does not adhere to.

FIG. 11B shows another possible tooling arrangement, in which there isprovided a potting cap 88 that is separate and distinct from the pottingtool fingers 78. During the potting process, the potting cap 87 canserve to limit the flow of resin. After the resin has hardened, thepotting cap 87 can be removed. The potting cap 88 may be reusable, suchas for example by being made of a material that the potting materialdoes not adhere to. In FIG. 11B, for clarity of illustration, thepotting cap 88 is shown displaced upward from where it would normally belocated. During use, the actual orientation would be such that pottingcap 87 would be in contact with the corresponding surface of pottingtool fingers 78. Potting cap 87 may have an inlet orifice 87A. The inletorifice 87A may be such as to allow resin to be introduced into thepotting cap and into the regions around the fibers that are to bepotted.

As part of the potting process, centrifugation may be used. In such aprocess, the cartridge may be spun while the potting material is beingintroduced into the cartridge, while the potting material is curing, orboth. The centrifugal force created by the spinning may urge the resinto the ends of the cartridge, where it can harden. Centrifugation can beconvenient if both ends of the cartridge are of similar or identicaldesign. In this way, both ends of the cartridge can be potted during asingle manufacturing operation. The resin can, for example, bepolyurethane. An alternative potting process would be by gravity drivenpotting, in which case the respective ends of the cartridge would haveto be potted one end at a time.

Referring now to FIG. 12A, when potting material 84 has completelycured, the filter assemblage is removed from the potting tooling, andany potting material 84 and fiber bundle 68 extending beyond tube end 66of housing 60 is cut away, thus re-exposing the lumens of the filterfibers. Polishing may also be performed. Because the fibers of fiberbundle 68 are now securely held in place by potting material 84, voidflow channels 82 remain in fiber bundle 68 at least where the pottingtool fingers had been, and radial channels 86 remain in potting material84 in those locations that had been occupied by the potting tool fingers78. It can be appreciated, as best seen in FIG. 12A and FIG. 13, thatthere can be both a void flow channel 82 in the fiber bundle and aradial channel 86 in a portion of the potting material 84, and these twofeatures may be somewhat continuous with and in communication with eachother. Both the radial channels 86 and the void flow channel 82 may beformed as space that is complementary to the potting tool finger 78.

It can further be appreciated, as illustrated in FIGS. 12A and 12B, thatthe pattern of rearrangement of fiber locations may extend through someextent of the potting material 84 in the axial direction, and maymanifest itself at the surface of the potting material 84 that faces theend cap, i.e., faces away from the midplane of the cartridge. FIG. 12Ashows a possible situation in which the disturbances in the fiberrearrangement, i.e., void flow channels 82, are slightly visible in thesurface of potting material 84. It can be noted that the exposed surfaceexposing the lumens of the fibers would be a cut and polished surface,polished such that the lumens of the fibers are accessible for fluidcommunication with the lumens. In FIG. 12A, the void flow channel 82 isvisible on that polished surface in the form of a narrow formationresembling a line, indicating that there is some but very littleremaining influence of the pattern of rearrangement of the fibers due tothe potting tool fingers 78.

FIG. 12B is similar to FIG. 12A but shows a possible pattern of fiberlumens at the outward-facing surface of the potting material 84 if thecutting and polishing of the potting material 84 were done a little bitcloser to where the potting tool fingers 84 had been placed. In thissituation, on the cut and polished surface, there could be identifiableregions containing substantially no fibers, and those regions could haveshapes and positionings that would roughly resemble the shapes andpositionings of the potting tool fingers 78. The pattern of fiberabsence in the surface of the potting material 84 might possibly benarrower or less distinct than the shape of potting tool fingers 78, butwould be more distinct or more visible than the pattern in FIG. 12A. Thenumber of such shapes would be expected to be the same as the number ofpotting tool fingers 78. In FIG. 12B those regions containingsubstantially no fibers are illustrated as being triangular in shape,being wider at the outer circumference of the fiber bundle and taperingupon proceeding radially inward. This is based on the assumption thatthe potting tool fingers also have a shape that is at least somewhattriangular when viewed along the longitudinal axis of the cartridge.

It can be further appreciated that the pattern of void flow channels 82due to rearrangement of fibers in the fiber bundle region may have somesymmetry. For example, the fiber void flow channels 82 may besubstantially equiangularly spaced around the circumference of the fiberbundle and may be substantially identical to each other. Thisillustrated pattern of the fiber void flow channels 82 may beadvantageous in achieving a uniform and rapid transition anddistribution of flow into the fiber bundle as uniform axial flow.However, it can be understood that other patterns are possible andsymmetry is not essential.

It can be appreciated that there is a difference between the views ofthe potting material seen in FIGS. 12A-12B, and the views of the pottingmaterial seen in FIGS. 12C-12F. FIGS. 12A-12B illustrateoutwardly-facing surfaces of the potting material. The termoutward-facing refers to the fact that the particular surface facesoutwardly away from the midplane of the cartridge. FIGS. 12C-12Fillustrate inwardly-facing surfaces of the potting material, referringto the fact that the particular surface faces inwardly toward themidplane of the cartridge and toward the inter fiber space. The views ofFIGS. 12C-12F include sectional cuts through the fibers.

FIG. 12C illustrates the appearance of an inwardly-facing surface of thebarrier composed of the potting material 84. The inwardly-facing surfaceof the barrier faces the inter fiber space and the mid region of thecartridge. The surface visible in FIG. 12C is not polished, and actuallyhas fibers protruding through it or emerging from it. It can beappreciated that in the view represented by FIG. 12C, and because of themanufacturing method illustrated involving the potting tool fingers 78,the surfaces that are visible in FIG. 12C might not all be coplanar witheach other. Rather, in the illustrated cross-section, the visiblesurfaces that lack fibers may be recessed with respect to the visiblesurfaces that contain fibers. In regard to FIG. 12C, it can be explainedthat because FIG. 12C is a sectional view taken with a viewing directionas illustrated in FIG. 12A, the sectional cut cuts through the fibers sothe view shows a cut surface of the fibers; but the radial channel islocated at a different axial position with respect to the longitudinalaxis of the cartridge, and so the sectioning plane would not actuallycut through the potting material at the location of the radial channel.FIG. 12C illustrates the inwardly-facing surface of the potting materialfor the same construct as was illustrated in FIGS. 12A-12B.

In regard to FIGS. 12A-C, given potting tool fingers as illustrated, itwould be possible, if the fill level of the potting material were chosenappropriately, to have the inward-facing surface of the potting materialexactly match the corresponding surface of the potting tool finger oreven have a gap between the potting material surface and thecorresponding surface of the potting tool finger. In such a situation,there would be void follow channels 82 in the fiber bundle while therewould not be any radial channel 86. However, in FIGS. 12A-B, thepresence of radial channel 86 is illustrated, partly as a matter ofmanufacturing convenience.

Referring now to FIGS. 12D, 12E and 12F, there are shown additionalpossible sectional views with the same point of view and sectiondefinition as FIG. 12C. FIGS. 12D-12F illustrate still more possiblepatterns of fibers as the fibers emerge from the potting material. Itcan be appreciated that patterns similar to those of FIGS. 12D-12F couldexist on the cut and polished outward-facing surfaces of the pottingmaterial, although the patterns might not be as pronounced as in FIGS.12D-12F.

Referring now to FIGS. 12D and 12E, there are shown embodiments thatwould be created by potting tool fingers that are not all of equal size.Such a design is prompted by the realization that as the void flowchannels proceed toward the interior of the fiber bundle, the void flowchannels come closer to each other (i.e., closer than they are to eachother near the outer circumference), and this close approach might notprovide much additional benefit. Therefore, an alternative arrangementof the potting tool fingers would be an arrangement in which some of thepotting tool fingers are one length and others of the potting toolfingers are another, different length. As illustrated, in such asituation, half of the potting tool fingers are longer and go moreradially inward from the outer circumference, and the other half of thepotting tool fingers are shorter and do not go as far radially inwardfrom the outer circumference. For example, the longer potting toolfingers may extend more than half of the radial distance inward from theouter circumference, while the shorter potting tool fingers may extendless than half of the radial distance inward from the outercircumference. In FIGS. 12D and 12E, it is shown that the larger of thevoid flow channels come inward from the outer circumference by more thanhalf of the radial dimension of the housing, while the smaller of thevoid flow channels come inward by a lesser distance than do the largervoid flow channels. The smaller void flow channels come inward by lessthan half of the radial dimension of the housing. The longer void flowchannels and the shorter void flow channels may alternate with eachother, proceeding around the circumference of the fiber bundle. In FIG.12D, such an arrangement is shown for a total of 8 void flow channels (4large and 4 small). In FIG. 12E, such an arrangement is shown for atotal of 12 void flow channels (6 large and 6 small).

FIG. 12F shows yet another possible arrangement of void flow channels.In this arrangement, the void flow channels are not generally straightin a radially inward orientation as they were in FIGS. 12A-12E. Rather,FIG. 12F shows that the void flow channels could be curved. Suchcurvature could create a situation in which the separation distancebetween adjacent void flow channels varies less strongly as a functionof radius than is the case for the situation illustrated in FIG. 12A.The curving nature of the void flow channels (with the local slope ofthe outline of the void flow channel being closer to a tangentialorientation near the outside of the fiber bundle and closer to a radialorientation further inward in the fiber bundle) may partially althoughnot completely compensate for the changing size of the fiber bundle as afunction of radius. Such void flow channels could be produced by pottingtool fingers that are curved similarly to the illustrated void flowchannels. Such potting tool fingers, if they are curved in the form of acircular arc as illustrated, could be swung into place by rotationaround the respective centers of the respective circular arcs.

FIGS. 12A-12F mostly described patterns of fibers as visible on one oranother surface of the potting. In addition, embodiments of theinvention also pertain to the distribution of fibers in the inter fiberspace near the potting. The spatial distribution of fibers may benon-uniform in a pattern that is intentional and is created when pottingis performed, specifically, when the resin solidifies. Specifically,this pattern may feature fiber-free regions that correspond to flow voidchannels, and, in places other than the fiber-free regions thatcorrespond to the flow void channels, these embodiments may feature mayfeature a relatively uniform distribution of fibers.

It can be noted that the distributions of fibers in three-dimensionalspace as discussed here, such as void flow regions, are built in to thefiber bundle and are not the result of random “clumping” of fibers assometimes occurs in dialyzers (especially when the fibers of thedialyzer become wet on their outsides). In fact, cartridges ofembodiments of the invention may be designed having features that arespecifically intended to discourage the random “clumping” of fibers atplaces other than the intended void flow channels. Features that help toavoid random “clumping” of fibers include the use of wavy fibers and theuse of specific void fractions as discussed elsewhere herein. The voidflow channels may be created specifically as a result of the pattern offibers where and when the fibers are immobilized at the place where thefibers enter the potting, at the time of hardening of the pottingmaterial.

The use of the potting tool fingers as already described may determineseveral geometric facts that may influence the long-term position of thefibers near the void flow channels. First, the potting tool fingers maydetermine the x-y location of the fibers at the place where the fibersemerge from the interior-facing surface of the potting material. (X-yrefers to two Cartesian directions generally along a planar oralmost-planar surface of the potting material.) Second, the potting toolfingers may determine the angle at which the fibers emerge from theinterior-facing surface of the potting material. Commonly, this anglemay be at least approximately parallel to the longitudinal axis of thecartridge, and such parallelism would especially be true if the surfacesof the potting tool fingers are substantially parallel to thelongitudinal axis of the cartridge at or near the place where thepotting tool fingers meet the interior-facing surface of the pottingmaterial. However, it is not absolutely necessary that the surfaces ofthe potting tool fingers, or the fibers themselves, be exactly parallelto the cartridge longitudinal axis at this location. Finally, thegeometry of the potting tool fingers can help to determine the exactlength of particular fibers from the emergence of the fiber at onepotting end to the emergence of the same fiber at the other potting end.(This discussion does not consider possible waviness of the fibers.) Ofcourse, this fiber length would nominally be the distance from theinterior-facing surface of the potting at one end to the interior-facingsurface of the potting at the other end. However, it would be possiblefor such fiber length to be slightly longer than the nominal distance,possibly influenced by the details of fanning of the fibers and also howthe potting tool fingers displace the fiber. It can be appreciated thatthe distance to which the fiber bundle continues to exhibit the“disturbance” introduced by the potting tool features can be influencedby all of these factors, i.e., the x-y positioning of the emergence ofany particular fiber from the potting, the angle of emergence ofparticular fibers from the potting, and the constrained length of aparticular fiber. It can further be appreciated that the extent of thepersistence of the “disturbance” in the fiber bundle also could beinfluenced to some extent by the stiffness or flexibility of the fibers,which would affect how they respond spatially to being displaced by thepotting tool fingers. Yet another parameter that could possiblyinfluence the positioning of the fibers in the potting might be how muchextra length is provided for the fibers prior to potting and subsequentcutting-off of the fibers. This extra length could influence thepositioning, especially the angular positioning, of the fiber ends. Allof these parameters can be chosen so as to achieve a desired geometry ofthe void flow channel(s) in the fiber bundle.

It can be noted that the interior-facing surface of the potting may beidealized as a plane or may be at least approximately a plane. However,at a more exact level of detail, the interior-facing surface might havea slight curvature to it, especially if the potting process is acentrifugal potting process, and more particularly if the axis forspinning during the centrifugal potting process goes through themidpoint of the length of the cartridge, which would typically be thecase if both ends of the cartridge are potted simultaneously.

By virtue of the potting, the position of the fibers immediately as theyemerge from the potting is known. However, by the nature of the fibersbeing long and slender, the position of the fibers elsewhere in theinter fiber space is not so definite. More generally, as a descriptionof the fiber placement in three-dimensional space within the fiberbundle, the pattern displayed on the potting interior-facing surfacewhere the fibers emerge from the potting, may continue for some distancein the fiber bundle exhibiting void flow channels, but may eventuallytransition into a different distribution that may be more uniform thanthe pattern and distribution that exist immediately adjacent to thepotting. This transition may happen together with a geometric fanning ofthe fibers. It is possible that the void flow channels may exist only inthe fanning region of the fiber bundle, perhaps only in a portion of thefanning region of the fiber bundle. The unfanned region of the fiberbundle may have fibers that are substantially uniformly distributed.

To the extent that the geometry of voids and fibers near the cartridgeend can be defined, and it is defined to at least some extent, the voidflow channel, first of all, may have a principal direction thatdescribes the path inward from the perimeter of the fiber bundle towherever the void flow channel ends inside the fiber bundle or reachesmost interiorly inside the fiber bundle. Additionally, the void flowchannel may have a transverse dimension that is measured generallyperpendicular to the principal direction of the void flow channel. Thetransverse dimension may generally be tapered, being greater at theperimeter of the fiber bundle and smaller more interiorly in the fiberbundle. Such tapering may be consistent with the expectation that asflow proceeds inwardly along the principal direction of the void flowchannel, some of the flow would exit from the void flow channel into thefiber bundle adjoining the void flow channel. (This description appliesto a flow inlet end of the cartridge; the opposite would be true at aflow exit or discharge end of the cartridge.) The void flow channel alsomay have a tapering in the axial direction proceeding away from thepotting interior-facing surface. Such tapering may result from a naturaltendency of the fibers to assume a more uniformly-spaced configuration,or from the fanning configuration of the fibers as imposed by theinterior shape of the housing, or both.

Referring now to FIG. 12G, there is shown a combined illustration of howthe local fiber porosity could vary as a function of position along thelongitudinal axis of the cartridge, taking into account various featuresdescribed herein. What is illustrated in FIG. 12G is most directlypertinent to the situation illustrated in FIGS. 12A, 12B and 12C,although in general such an illustration could be constructedrepresenting any of the designs illustrated in FIGS. 12A-12F. What isplotted in FIG. 12G is the local porosity fraction within thefiber-occupied portions of the fiber bundle. The term “fiber-occupiedportions of the fiber bundle” is intended to refer only to regions thatdo include fibers spaced near each other, while ignoring void flowchannels if void flow channels are present.

The fiber bundle can be divided into three regions along thelongitudinal direction of the cartridge, going from the midplane to anend of the cartridge, along with a fourth region that contains pottingmaterial. It can be pointed out that the central region of thecartridge, designated Region I, has a substantially uniform insidediameter of the housing and a substantially uniform packing fraction ofthe fiber bundle. The porosity in Region I can be referred to as thecentral porosity. Proceeding longitudinally away from the cartridgemidplane, there is Region II, in which there is fanning of the fibers,i.e., the housing interior starts to taper so as to increase theinternal cross-sectional area and the porosity fraction. In Region IIthere may be or there might not be influence of the potting tool fingersor the void flow channels created by the potting tool fingers. Asillustrated In FIG. 12G, there is some influence in part of Region IIand no influence in another part of Region II. The porosity in Region IIcan be referred to as the transitional porosity. At any givencross-section, this porosity can be considered to be the empty spacebetween fibers not counting the identifiable void flow channels, dividedby the space within the housing not counting the identifiable void flowchannels. Thus, this porosity is essentially a descriptor of thedistance of a fiber that is locally in a bundle configuration, to itsnearest neighbor fibers. Next, there is Region III, in which there isboth fanning of the fibers and the presence of the potting tool fingersand the associated void flow channels. The porosity of the fibers wherethe fibers emerge from the potting is the end porosity. It may becalculated just as the transitional porosity was calculated, omittingidentifiable void flow channels.

There is also illustrated, in FIG. 12G, a Region IV that is inside thepotting.

This region does not affect the flow distribution in the inter fiberspace, because in Region IV there is potting material rather than openspace for fluid to flow. Nevertheless, the fanning of the fibers withinthe potting material can be expected to continue in approximately thesame pattern exhibited in Regions II and III.

For the sake of a numerical example, this design may be discussedassuming that the porosity of the fiber bundle at the mid-region ormidplane of the cartridge is 50%, and it may be assumed that at themid-region or midplane the inside diameter of the cylindrical housing is1 unit and the inside area of the cylindrical housing is 1 unit. Thus,the area occupied by the fibers would be 0.5 units and the void areaalso would be 0.5 units. This would describe the entirety of Region I upto the boundary with Region II. Further, it may be assumed that at theend of Region II, the inside diameter of the housing has increased to1.1 units. Thus, the internal area has increased to 1.21 units, whilethe area occupied by the fibers remains at 0.5 units, so the area notoccupied by the fibers would be 0.71 units. Thus, the porosity would be0.71/1.21 or 59% if there is no spreading of fibers in Region II carriedover from the potting tool fingers.

It may further be assumed that in Region III the tapering of the housinginterior continues to increase so that at the end of Region III, theinside diameter is 1.2 units. Thus, the internal area would be 1.44units, of which 0.5 units would be fiber cross-sectional area and 0.94units would be empty space. So, if fibers were distributed throughoutall of that space and there were no potting tool fingers orcorresponding void flow channels, the porosity would be 0.94/1.44 or0.65. However, it may be assumed that the potting tool fingers and thevoid flow channels created thereby occupy some space, which may beassumed to be 0.05 units. Thus, the actual empty space between fibers is1.44−0.50−0.05 or 0.89 units. So, the porosity fraction would be0.89/1.44, or 0.62. It can be seen with this numerical example that inRegion III as one proceeds from the boundary between Region II andRegion III, the porosity continues to increase toward the end of thecartridge, but only slightly. How much the porosity increases and,whether it increases at all, depends on the size of the potting toolfingers and the void flow channels. This illustrates that the size ofthe potting tool fingers can have an important influence on the localporosity of the fiber bundle. The porosity just calculated for RegionIII is for the fiber bundle of Region III omitting the void flowchannels. The void flow channels are omitted from the calculationbecause the void flow channels are intended to serve an entirelydifferent purpose, namely distributing flow easily from place to placewithin the cross-section of the fiber bundle. For present discussion theporosity fraction is intended to be illustrative of the local conditionsof blood flow among fibers in the inter fiber space. This could bethought of as an analogy between local flow among the fibers and localflow through a porous medium, for which local porosity among the fiberswould be an important descriptive parameter. For example, if the pottingtool fingers were larger than just assumed, they might make the porosityof Region III where fibers are spaced next to each other smaller thandesired. Indeed, if the assumed amount of space devoted to the void flowchannels was a few percentage points larger than just assumed, it couldmake the porosity of Region III smaller than the porosity of Region II.The void dimensions and the geometry of the fanning-out of fibers may berelated such that the local porosity fraction within the fiber-occupiedportions of the fiber bundle is either constant or increasescontinuously from mid-cartridge out to the end of the cartridge. Forexample, it may be desirable to have the inside diameter of the housingnear its end increase to a value that is larger than the factor of 1.2that was just assumed. In Region IV, the fibers may continue along thetrajectory that they had in Region III and may have substantially thesame slope as in Region III, but the fibers are potted in the pottingmaterial. In Region IV, there is no flow past the outsides of thefibers.

Referring now to FIG. 13, the filter assemblage of FIG. 12 may becompleted by adding a dialysate cap 88, which may be bonded to the endof housing 60 along circumferential cap-tube joint 94, and then byadding sleeve 96, which may be bonded to cap flange 92 alongcircumferential sleeve-cap joint 100, and also bonded to tube flange 98along circumferential sleeve-tube joint 102. Sleeve 96, cap flange 92,tube flange 98, and the exterior of housing 60 may form acircumferential distribution channel to distribute a patient's blood (orto distribute other fluid) uniformly to a plurality of radial openingscomprising radial ports 64, void flow channels 82 and radial channels86. Alternatively, other designs could also provide a circumferentialdistribution channel and appropriate joining of parts.

This cartridge as constructed may have the property that it may providea plurality of unobstructed radially oriented flow channels such as voidflow channels 82 that provide a flowpath in a generally radial directionto allow flow to readily penetrate radially into the interior of fiberbundle 32. It is expected that as a result of the presence of the voidflow channels 82, the overall flow entering the fiber bundle cantransition to a uniform axial flow within the fiber bundle 32, within amuch smaller region or axial distance than would be required for thesimpler cartridge depicted in FIG. 6. In the configuration illustratedin FIG. 13, if there occur any regions within the fiber bundle havingstagnation or low flow velocities, it can be expected that the size ofsuch stagnation or low flow regions will be much smaller than wouldoccur in a prior art cartridge. If similar geometry is provided at theexit or discharge end of the cartridge, similar behavior can also beexpected at that end.

For understanding geometric proportions and relationships, it may beunderstood that the fibers in the fiber bundle may have an averagefiber-to-fiber spacing at a mid-region of the cartridge, such as midwaybetween the two ends of the cartridge. In the void flow channels 82,near an end of the cartridge, the fiber bundle may contain at least onesubstantially open void flow channel 82 that has a transverse dimension,at at least some location, that is at least 5 times the averagefiber-to-fiber spacing that occurs at the mid-region of the cartridge.The void flow channel may have a transverse dimension, at at least somelocation, that is at least 3 times the average fiber-to-fiber spacingthat occurs at the mid-region of the cartridge, or at least 5 times, orat least 10 times the average fiber-to-fiber spacing that occurs at themid-region of the cartridge.

It can further be understood that at the place where fibers emerge fromthe potting to become the fiber bundle, the void flow channel is welldefined because the location of the fibers is well defined by thepotting. As one proceeds away from the end of the cartridge and thepotting, and approaches relatively closer to the middle of thecartridge, the void flow channel 82 may become narrower or less welldefined because the fibers have some flexibility and there is someopportunity for the fibers to rearrange themselves more uniformly. Asdistance away from the potting increases, the influence of fiberposition at the potting, as determined by the positions of the pottingtool fingers 84 in arranging the positions of the fibers, can beexpected to diminish. The distribution of the fibers as a function ofdistance away from the potting may also be influenced by the shape (e.g.taper) of the potting tool fingers 84. Indeed, it may be desirable thatin most of the middle region of the cartridge occupying a large fractionof the length of the cartridge, except for void flow channels 82, thefiber bundle be substantially uniformly distributed within the housing.It is believed that, other than at the transition region that includesthe tapered housing interior and the void flow channels 82, it isdesirable to have substantially uniform distribution of fibers withinthe housing.

It is possible that the fiber void flow channel 82 could be tapered inthe radial direction, being wider near the outer circumference of thefiber bundle and narrower closer in toward the longitudinal axis of thefiber bundle. This can be understood from the shape of the potting toolfingers 78 illustrated in FIG. 9, which cause the fibers to bedistributed so as to form the void flow channel 82. It is furtherpossible that the void flow channel 82 can be tapered in the axialdirection, being wider near the potting material and narrower away fromthe potting material. This also can be understood from the shape of thepotting tool fingers 78 illustrated in FIG. 9. It can be seen in FIG. 9that the potting tool fingers 80 are wider closer to the end of thecartridge and taper to a sharper shape having relatively narrowthickness at a location closer to the midplane of the cartridge and thefiber bundle.

As further examples of possible numerical parameters, in embodiments ofthe invention such as this first embodiment, the length of cartridge canbe in the range of approximately 150 mm to approximately 300 mm orslightly longer. The total surface area of the hollow fiber membranescan range from 0.1 m² (which might correspond to a dialyzer forpediatric hemodialysis) to 3 m² (which would be at the upper end of therange of dialyzers for adult hemodialysis). The outside diameter of thehousing (at or near the midplane of the cartridge) may vary in the rangeof approximately 20 mm to approximately 50 mm. If a cartridge at itsmidplane has an inside diameter of 35 mm, then the internalcross-sectional area of the housing is about 960 mm².

The fanning angle of the fibers, where fanning exists, could be in therange of 5 to 15 degrees, perhaps typically 10 degrees. This anglerepresents the slope of the outermost fiber relative to the centerlineof the cartridge. The ratio of the cross-sectional area of the fiberbundle at ends of the fiber bundle, relative to the cross-sectional areaat the start of fanning of the fibers, depends on the fanning angle andalso on how long the fanned region is. Such area ratio could be in therange of 1.1 to 1.7.

The length of the end region of the cartridge (including fanning, andthe features that make up an orbital distributor, and the dimensions ofthe potting tool fingers) could be such that approximately 10% of theoverall length of the cartridge may be allocated to an end transitionregion at one end of the cartridge, and another 10% of the overalllength of the cartridge may be allocated to an end transition region atthe other end of the cartridge, and the remaining 80% of the overalllength of the cartridge may be allocated for the middle region that isuniform and of constant cross-section, or nearly uniform and of nearlyconstant cross-section. Corresponding actual dimensions could be alength of 30 cm for the middle region and 2.5 cm to 3 cm for each of theend regions. Of course, these dimensions could be varied as desired.

In regard to the potting tool fingers, if it is assumed that there aresix such fingers and they have an extent of 2 mm along the circumferenceof the fiber bundle, and the voids are triangular extending inward forhalf of the radial dimension of the fiber bundle, and if the diameter ofthe fiber bundle is 40 mm, then the total cross-sectional area of thesix of them would occupy about 5% of the cross-sectional area of thefiber bundle. This is approximately what was assumed in hypotheticalcalculations discussed in connection with FIG. 12G.

It might be considered that a channel whose entrance is 2 mm wide is notas wide as might be desired, in view of various flow properties ofblood. Accordingly, additional possible dimensions and dimensionalcombinations are presented here. In another possible set of dimensions,the diameter of the fiber bundle at the cartridge midplane might be 4 cmand the diameter of the fiber bundle at the potting might be 5 cm.Compared to the previous example, this numerical set of fanningparameters gives a somewhat greater expansion providing space for largervoid flow channels. These two diameters provide a diameter ratio of 1.25and an area ratio of 1.56. The cross-sectional area of the fiber bundleat the midplane is 12.56 cm2, and the cross-sectional area of a 5 cmdiameter circle is 19.6 cm2, which is 7 cm{circumflex over ( )}2 greaterthan the midplane cross-sectional area. If there were six void flowchannels of triangular cross-section, and the base of each triangle were1 cm measured along the circumference of the fiber bundle and the heightof the triangle were 2 cm extending radially into the fiber bundle(compared to a fiber bundle radius of 2.5 cm at the location of the voidflow channels), then the area of each such triangle would be 1 cm2 andthe total area of the six void flow channels would be 6 cm2. This 6 cm2total cross-sectional area of the void flow channels is about 30% of theassumed total cross-sectional area of the fiber bundle at the end. Thiswould leave (19.6 cm2-6 cm2) or 13.6 cm2 of cross-sectional area foractual fiber bundle, which still is larger than the unfanned cartridgecross-sectional area of 12.56 cm2 at the midplane. So, even with somecross-sectional space being devoted to void flow channels, the fiberspacing in the actual grouped fibers still exhibits some fanning, i.e.,some increase in local porosity or void fraction compared to the spacingof the fibers at the cartridge midplane. This is believed to bedesirable. Of course, still other combinations of dimensions could beenvisioned. For example, the circumferential dimension of a void flowchannel at the outside circumference might be in the range of 3 mm to 10mm, more specifically 4 mm to 7 mm. Choice of this dimension could beinfluenced by whether the fluid intended to be flowing in the interfiber space is ordinary blood, anticoagulant-treated blood, ordialysate.

Still further discussion of fanning properties can be given here. Thefanning angle of the outermost fibers in a fiber bundle may be in therange of 5 to 15 degrees, typically somewhere around 10 degrees. Atypical diameter of a fiber bundle is 4 cm for sake of example. Thelength of the fanning region at any individual end of the cartridge canbe in the range of 1 cm to 2.5 cm. This can provide an increase indiameter of the fiber bundle of from an initial 4 cm diameter to a final4.2 cm diameter, or a final 4.4 cm diameter, or even a final 5 cmdiameter. The fanning may be defined at least partially by an internalshape of the housing. The fanning does not have to be strictly a conebut could be any shape that provides gradual enlargement ofcross-section as a function of distance along the longitudinal axis ofthe cartridge. Fanning can be described by a geometric fanning factor,which may be simply determined by the housing interior geometry such asby diameter ratios. For example, a diameter ratio of 1.25 to 1 gives ageometric fanning factor of 1.56, as discussed. In embodiments of theinvention, the geometric fanning factor may be generally in the range of1.1 to 1.7, more specifically in the range of 1.3 to 1.6. There may alsobe calculated a void-adjusted fanning factor. A void-adjusted fanningfactor may describe the gradual change of the flow situationrepresenting flow between neighboring fibers. For example, if there isgeometric fanning but essentially all of the increase in cross-sectionalarea is devoted to void flow channels, then the actual spacing betweenneighboring fibers would not change and this fact would be representedby the void-adjusted fanning factor. The void-adjusted porosity at theend, adjacent to the potting material, may be defined as (totalcross-sectional area of fiber region excluding void flow channels, minustotal cross-sectional area of fibers), divided by (total cross-sectionalarea of fiber region excluding void flow channels), This may be comparedto the porosity at the midplane. In embodiments of the invention, thevoid-adjusted porosity at the end may be greater than the midplaneporosity by a factor of at least 1.1, or at least 1.2, or 1.3, or 1.4.

Regarding materials of construction, for the housing, polycarbonate andpolypropylene are commonly used. For the potting material, a commonchoice is polyurethane. The hollow fibers can be made of any of variouspolymeric materials that are known for use in such fibers. Examplesinclude polyethersulfone in combination with polyvinylpyrrolidone;polyacrylonitrile; cellulose triacetate; polyether polymer alloypolymethylmethacrylate; and other substances.

In the first embodiment as just described, the discussion has beenpresented as applied to the configuration in which blood flows in theinter fiber space and dialysate flows in the fiber lumens. It isappropriate, for this configuration, to pay especially close attentionto the flow field of liquid, i.e., blood, flowing in the inter fiberspace. The reason is that blood has a preferred range of shear rate andshear rate gradient. Some phenomena to be avoided are blood formingclots, and leukocytes segregating out from the flow. Specifically, ithas been observed experimentally, with blood flowing in the inter fiberspace, that the location where clots are most likely to form in theentire cartridge is at the first few layers of fibers where the bloodenters the fiber bundle from the orbital distributor. It is believed(although it is not wished to be limited to this explanation) that thetendency for clots to form at that particular location may be related tothe sharp change of shear rate experienced by the blood as the bloodleaves the relatively wide open channel flow of the tubing and theorbital distributor, and enters the narrow interstices of the interfiber space. It is further believed (although not wishing to be bound bythis theory) that if there is a transition of local porosity as afunction of position generally along the flowpath, this will provide amore favorable condition for blood flow to be introduced into the fiberbundle thereby avoiding clotting and sequestration of leukocytes.

It also can be kept in mind that this embodiment, and generally thevarious embodiments herein, are in general a vehicle for providing amore uniform and rapidly-equilibrated flow of liquid in the inter fiberspace. The first embodiment provides a transition from flow enteringthrough a side port, to generally axial flow in a majority of the lengthof the cartridge. The liquid in the inter fiber space does not have tobe blood. If desired, that liquid flowing in the inter fiber space couldbe dialysate, instead of blood. Even for conventional dialysis systemsin which the inter fiber space contains dialysate, it is known that theproblem of achieving truly uniform flow of dialysate has not beencompletely solved in the prior art, and the nonuniformity of dialysateflow has an unfavorable impact on the efficiency and clearance of thedialyzer simply. Accordingly, it is possible to use embodiments of theinvention in a configuration such that dialysate flows in the interfiber space, simply for the purpose of improving the uniformity of thatflow of dialysate.

It is believed that having the porosity continuously decreasing uponprogressing along the longitudinal direction is useful for the situationwhere blood flows in the inter fiber space. This is becauseexperimentally there has been some observation of clotting occurring atthe entrance to the fiber bundle from an orbital distributor. The ratioof maximum porosity in the end region, to the mid-region porosity, maybe chosen so as to achieve desired results in such regard as avoidingthe formation of blood clots in the inter fiber space (if blood is thefluid flowing in the inter fiber space). This may be done by achieving adesired shear rate or shear rate gradient for the blood flow at theentrance to the inter fiber space. The orbital distributor used with thecartridge may be of any desired design, such that it serves todistribute the flow to substantially the full circumference of the fiberbundle.

Overall, a description of the lengthwise features of the cartridge maybe such that approximately 10% of the overall length of the cartridgemay be allocated to an end transition region at one end of thecartridge, and another 10% of the overall length of the cartridge may beallocated to an end transition region at the other end of the cartridge,and the remaining 80% of the overall length of the cartridge may beallocated for the middle region that is uniform and of constantcross-section, or nearly uniform and of nearly constant cross-section.

Embodiment 2

A second embodiment of the invention is illustrated in FIGS. 14-18. Thecompleted cartridge of this embodiment is depicted in FIG. 18. Methodsof manufacturing such a cartridge are illustrated in FIGS. 14-17A. Muchof the discussion about void flow channels from the first embodimentalso applies to the second embodiment, with the difference being achange of the geometric orientation by which the void flow channelsapproach the fiber bundle. In this embodiment, the flow into the interfiber space is introduced in a generally axial direction. Thus, theequilibration of this flow may require some spreading out from thepoint(s) of introduction, but there is no overall large change ofdirection of this flow. This lack of change of direction of the flow isa contrast to what was present in the first embodiment (in which theflow underwent a directional change of approximately 90 degrees). It canbe appreciated that in this second embodiment, the introduction of theflow that goes through the inter fiber space, and introduction of theflow that goes through the lumens of the fibers, are in flow directionsthat are substantially aligned with each other.

As discussed in connection with the first embodiment, it is againbelieved that in order to avoid clotting and other undesirable phenomenawith regard to introducing blood flow into the inter fiber space (ifblood is the fluid flowing in the inter fiber space), it is desirable tominimize sudden change in the shear rate of the flowing blood.

A cartridge of this embodiment of the invention may be constructed inaccordance with the following steps.

Referring now to FIG. 14, a housing 106 may have a tapered end portion,and may be filled with a fiber bundle 112. This internal taper isfavorable for creating fanning of the fibers near the end of thecartridge. FIG. 14 shows a housing that is internally tapered near anend, but on the outside is generally cylindrical. Discussion inconnection with FIGS. 7A and 7B is also applicable here. It would alsobe possible for the housing 106 to be internally tapered and externallytapered similar to what was shown in FIG. 7B. Preferably, at this stage,fiber ends 114 extend a short distance beyond housing end 110 of housing106. The fibers may have already had their ends closed, or the fibersmay be subjected to a closing operation at this stage of themanufacturing process.

In FIG. 15, a potting cap 116 may be applied to the filter assemblage ofFIG. 14. A circumferential potting sleeve 118 may then slip over theoutside of housing 106. Potting cap 116 may contain a receiving orificeand manifold 140 for receiving potting resin and distributing itthroughout the region that is to be potted. A potting cap end 120 may bepositioned a short distance beyond filter fiber ends 114. Potting capend 120 may support a plurality of fiber displacement fingers 122. Fiberdisplacement fingers 122 may comprise a finger shoulder 124 having asubstantial diameter, and may comprise a finger extension 126 having alesser diameter. Finger extension 126 may preferably be tapered, forexample, conical, and may end in a blunt tip 128. Fiber displacementfingers may be advanced in a longitudinal direction with respect to theoverall cartridge. Potting tool fingers in Embodiment 1 and fiberdisplacement fingers in Embodiment 2 could generally be referred to asfingers or displacers, because of their role in displacing the positionsof fibers near them. As discussed in connection with another embodiment,it is possible for the fiber displacement fingers 122 to deliver a flowof a gas before, while or after they are being advanced into the fiberbundle. It is also possible that gas could be caused to flow through thefiber bundle itself as these operations take place. As discussed, notonly can such process steps and features avoid damaging individualfibers, but they may present another advantage also. They may encouragethe fibers to become uniformly spaced in the remaining space of thefiber bundle, as opposed to having a “bunching-up” featuring anincreased local packing density near the potting tool finger.

As discussed in connection with another embodiment, the viscosity of thepotting material 180, as it is injected, may be chosen such that thepotting material 180 enters the open fiber lumens only to a minimaldistance. It is furthermore possible that the ends of the fibers may besealed prior to the potting operation. For example, the fiber bundle maybe cut to length by a laser cutting operation that also leaves the endsof the fibers closed shut as a result of the heat involved in thecutting process. When potting material 180 is fully cured, the pottingcap 116 may be removed.

Fiber displacement fingers 122 may displace filter fiber ends 114radially from fiber displacement fingers 122, the extent of thatdisplacement being defined by the diameters of finger shoulders 124. Asthe fibers of fiber bundle 112 are somewhat stiff, void flow channels130 are created within fiber bundle 112, around finger extensions 126,both adjacent to and immediately below finger shoulders 124.

Referring now to FIG. 16, potting material 132 may be introduced untilvoid flow channels 130, filter fiber interstitial space, and anyadditional space within potting cap 116 is filled as far as a leveldepicted by line L-L. The viscosity of the potting material 132, as itis injected, may be chosen such that the material enters the open fiberlumens only to a predetermined minimal distance.

Referring now to FIG. 17A, when potting material 132 has completelycured, potting cap 116 may be removed from the filter assemblage, andany potting material 132 and fiber bundle 112 extending beyond tube end110 of housing 106 may be cut away, thus re-exposing the filter fiberlumens. Because the fibers of fiber bundle 112 are now rigidly held bypotting material 132, void flow channels 130 remain in fiber bundle 112,and axial channels 134 remain in potting material 132 in those locationswhere fiber displacement fingers 122 previously resided. The void can betapered in the axial direction, being wider near the potting materialand narrower away from the potting material. This can be understood fromthe shape of the potting tool fingers 122 and finger extensions 126illustrated in FIG. 16. Again, the void flow channel in the fiber bundlemay be such that the void flow channel, at at least at some location,has a transverse dimension that is at least 3 times, or at least 5 timesthe average fiber-to-fiber spacing at the mid-region of the cartridge.The void flow channel in the fiber bundle may be such that the fibervoid flow channel, at at least at some location, has a transversedimension that is at least 3 times, or at least 5 times, or at least 10times or at least 20 times the averagefiber-centerline-to-fiber-centerline spacing at the mid-region of thecartridge. The transverse dimension of the void flow channel can betapered along the principal direction of the void flow channel, similarto the tapering of the void flow channels in the first embodiment. Anactual transverse dimension of the void flow channel or an actualtransverse dimension of the potting tool finger 122 or finger extension126 may range from one to several millimeters at a narrower end, toapproximately 3 to 10 millimeters at the potting material. The length ofthe fanning region may be similar to the length of the fanning regiondiscussed in Embodiment 1, such as a distance of 1 to 2.5 cm. Parameterranges for the geometric fanning factor and the void-adjusted fanningfactor may be similar to those for Embodiment 1.

Referring now to FIG. 17B, the fiber bundle can be divided into threeregions along the longitudinal direction of the cartridge, going fromthe midplane to an end of the cartridge, along with a fourth region thatcontains potting material. It can be pointed out that the central regionof the cartridge, designated Region I, has a substantially uniforminside diameter of the housing and a substantially uniform packingfraction of the fiber bundle. Proceeding longitudinally away from thecartridge midplane, there is Region II, in which there is fanning of thefibers, i.e., the housing interior starts to taper so as to increase theinternal cross-sectional area and the porosity fraction. In Region II asillustrated there is no influence of the potting tool fingers or thevoid flow channels created by the potting tool fingers. As illustratedIn FIG. 17B, there is some influence in part of Region III and noinfluence in another part of Region III. Next, there is Region III, inwhich there is both fanning of the fibers and the void flow channelscreated by the potting tool fingers. There is also shown Region IV, inwhich the fibers may continue along the trajectory that they had inRegion III and may have substantially the same slope as in Region III,but are potted in the potting material. In Region IV, there is no actualflow past the outsides of the fibers.

Referring now to FIG. 18, to complete the construction of this secondembodiment of a cartridge, distributor plate 138 may be first insertedinto filter cap 136, and may be bonded along circumferentialdistributor-cap joint 142. Filter cap 136 may then be assembled tohousing 106, and may be bonded along circumferential cap-tube-joint 144,with distribution tubes 140 inserted into axial channels 134 of pottingmaterial 132. Sealing at distributor tube-channel joints 146 may beachieved either by inserting the tapered distribution tubes 140 into thetapered axial channels 134, with sufficient force, or by the use of abonding agent. Tapered distribution tubes 140, or potting material 132,or the combination of them, may be chosen so as to provide sufficientsoftness or dimensional properties of at least one of those materials soas to create a seal for keeping the blood and the dialysate compartmentsseparate and isolated from each other.

Blood, entering blood inlet/outlet 150 of filter cap 136, flows throughdistribution tubes 140, through axial channels 134, into void flowchannels 130 in fiber bundle 112, where it enters the interstitialspaces between fibers in fiber bundle 112, establishing a uniform axialflow within a short distance. With the provision of a plurality of axialchannels 134 as described and illustrated, any possible areas of lowflow velocity, or stagnation, within fiber bundle 112 can be expected tobe small and limited.

As illustrated, the axial channels 134 may be provided in a quantity andin a geometric arrangement such that there are seven axial channels 134.One of the axial channels 134 is centrally located substantiallycoinciding with the longitudinal axis of the cartridge, and the othersix axial channels 134 are arranged in a hexagon-like distributionsurrounding the central axial channel 134. Such an arrangement providesa useful symmetry and good packing or spacing properties of the axialchannels 134. It is believed that this is helpful for achieving anearly-uniform velocity over the entire cross-section, and achieving itwithin a short distance. It can be appreciated that, alternatively,other numbers and patterns of axial channels 134 could be provided,subject to practical manufacturing considerations and otherconsiderations.

Dialysate entering dialysate inlet/outlet 148 readily flows into andthrough the lumens of the fibers of fiber bundle 112. As illustrated,the dialysate inlet/outlet 148 could be used in such a way thatdialysate could flow in either of two possible directions with respectto the blood flow. Thus, the relative flow of the blood and thedialysate could be either co-flow or counter-flow, as desired.

In both the first and second embodiments as just described andillustrated, the flow direction of the blood and the flow direction ofthe dialysate could be either counterflow (blood flow and dialysate floware opposite to each other) flowing generally parallel to each other butin directions that are the opposite of each other) or co-flowing(parallel and flowing generally the same direction as each other).

Embodiment 3

A third embodiment, illustrated in FIGS. 19 to 24, provides yet anotherway to achieve uniform flow distribution in the inter fiber space.Whereas the first two embodiments attempted to mitigate the effects ofnon-uniform blood flow in the interstitial space between the fibers of afiber bundle, by providing means to channel the blood into the interiorof the fiber bundle in close proximity to the potting material used toencase the fiber ends and creating flow of fluid (blood) along thelongitudinal (axial) direction of the fibers, in contrast this thirdembodiment utilizes a yet another flow pattern to achieve uniformity. Inthis embodiment, the flow of fluid (blood) in the inter fiber space isgenerally perpendicular to the fibers generally everywhere in thecartridge.

Referring now to FIG. 19, there is shown filter base 152, used in theconstruction of a flat cross-flow filter cartridge. Filter base 152comprises a filter base plate 154, with upstanding side walls 156 risingfrom opposing side edges of filter base plate 154. Upstanding end walls158 extend a short distance from side walls 156 along opposing top andbottom edges of filter base plate 154. Inlet/outlet ports 160 arepositioned on sidewalls 156. Upstanding flow diverters 162 are locatedon filter base plate 154, adjacent inlet/outlet ports 160, and are usedto spread incoming flows entering distribution chambers 164.

Additionally, as shown in FIG. 20, there may be provided a screen 170.Such screen 170 may be helpful for maintaining the fibers in generallythe region in which it is intended that they be located. Screen 170 alsomay be helpful in causing the flow to be distributed as desired. Screen170 may take the form of a wire mesh screen, or alternatively may be aportion of a perforated sheet material. Screen 170 may be supported atits ends by screen support ribs 166 extending from end walls 158 supportand capture one end of screen 170. Screen support grooves 168 in filterbase plate 152 may support and capture the edges of screen 170.

As shown in FIG. 21, a rectangular fiber bundle 172, having a bundlecross-sectional shape that is generally rectangular, may be placed onfilter base plate 154, between screens 170. At this stage ofmanufacture, fiber ends 174 may preferably extend a short distancebeyond end walls 158.

As shown in FIG. 22, after this step, cover 176 (which is shown as beingsemi-transparent) has been placed on top of upstanding side walls 156and upstanding end walls 158. Screen support grooves (not shown) in theunderside of cover 176 may support and capture the top edges of screens170. Cover 176 may be bonded to the tops of upstanding side walls 156and upstanding end walls 158 by means of solvent welding, adhesivebonding, ultrasonic welding, or other suitable means.

Referring to FIG. 23, the filter assemblage of FIG. 22 then may havepotting caps (not shown) applied to both filter ends 178, and pottingmaterial 180 may be injected, to fill all available free space and fiberinterstitial space to a distance indicated by lines L-L. As discussedherein in connection with another embodiment, the viscosity of thepotting material 180, as it is injected, may be chosen such that thepotting material 180 enters the open fiber lumens only to a minimaldistance. It is furthermore possible that the ends of the fibers may besealed prior to the potting operation. For example, the fiber bundle maybe cut to length by a laser cutting operation that also leaves the endsof the fibers closed shut as a result of the heat involved in thecutting process. When potting material 180 is fully cured, the pottingcaps may be removed.

As shown in FIG. 24, the filter construction may be completed by firstcutting away excess potting material 180 and any fiber bundle protrudingbeyond end walls 158, thus re-exposing the filter fiber lumens. Thisoperation, as illustrated on the lower end of the filter in FIG. 24, maybe performed on both ends of the cartridge. Finally, as illustrated onthe upper end of the cartridge in FIG. 24, a dialysate cap 182 may beapplied to each end of the cartridge, and may be bonded along the entiredialysate cap bond edge 188, by solvent welding or other suitable means.It can be noted that, for ease of illustration, FIG. 24 only shows halfof the fiber bundle with respect to the direction of blood flow. Theremaining half, as defined by a sectioning plane along a central planeof symmetry of the cartridge, is omitted. Also, FIG. 24 shows onedialysate cap but, for ease of illustration, does not show the seconddialysate cap.

Dialysate entering dialysate inlet/outlet port 184, may be approximatelyevenly distributed in dialysate header 186 formed between dialysate cap182 and filter end 178, then may flow as indicated through the lumens offiber bundle 172. At the opposite end of the filter, the dialysate maycollect in the header of the second dialysate cap (not shown), and mayexit through the second inlet/outlet port.

Blood from a patient may be introduced through inlet/outlet port 160,and may be steered by flow diverter 162 into both halves of distributionchamber 164, where it may transition into a uniform flow normal toscreen 170, passing through the first screen 170, through theinterstitial space in fiber bundle 172, in the direction indicated, inthe rectangular space defined by filter base plate 154, cover 176, andpotting material 180 at both ends 178 of the filter.

At the other end of the cartridge, similarly to the flow pattern for theend that is illustrated herein, blood may then pass through the secondscreen (not shown), collect in the second distribution chamber (notshown), and exit through the second inlet/outlet port (not shown).

In this embodiment, given that the blood flow is directed through thefilter fiber interstitial space in a direction perpendicular to thefiber axes, it is possible to design an inlet distribution structurethat transitions the blood flow to a uniform flow, without stagnationareas, before the blood enters the fiber bundle. A similar structure atthe outlet end can collect blood leaving the fiber bundle.

Embodiment 4

Yet another embodiment of the invention, which is a fourth embodiment,is illustrated in FIGS. 25-32. In this embodiment, the flow past thefibers again is generally perpendicular to the fibers. Morespecifically, the cartridge in this embodiment has a generallyaxisymmetric geometry and the flow flows past the fibers in a generallyradial direction with respect to the overall generally axisymmetricgeometry. In order to achieve the generally radial flow past the fibers,there may be provided a central void 232 (FIG. 31) forming a channelthat extends generally along the longitudinal axis, which may conductblood in an axial direction until the blood transitions to a radiallyoutward flow direction flowing past the fibers. On the outside of thefiber bundle, there may be a fluid collection space in the form of aradial filter screen, which allows fluid that exits from the fiberbundle to collect and transition toward the outlet of the housing. (Thisdescription is given assuming that blood enters the fiber bundle alongthe axis and exits the fiber bundle at the outside circumference of thefiber bundle. The opposite is also possible.

Referring now to FIG. 25, there is shown a filter screen used in theconstruction of this embodiment. This screen may comprise an inner wire192, which may be formed into a helix, and a plurality of longitudinalwires 194. Inner wire 192 is preferably a small diameter wire, woundwith a large spacing of the helical turns. Outer wires 194 maypreferably be larger diameter wire, and may be joined to inner wires192, on the outside of the helix, to form a radial filter screen 190having a substantial free area for flow in the axial direction.

Referring now to FIG. 26, there is shown a fiber bundle 198 that isinserted into radial filter screen 190. The length of fiber bundle 198is preferably greater than the length of radial filter screen 190, suchthat fiber bundle ends 200 extend a moderate distance beyond screen ends196.

As shown in FIG. 27, radial filter screen 190 and fiber bundle 198 maybe inserted into housing 202. Housing 202 is preferably of a lengthmidway between the length of axial filter screen 190 and fiber bundle198, such that axial filter screen 190 is entirely within housing 202,whereas both fiber bundle ends 200 extend a short distance beyondhousing ends 204.

In FIG. 28, a plurality of screen support ribs 206, extending inwardfrom the wall of housing 202, in close proximity to inner wire 192 ofaxial filter screen 190, may insure that axial filter screen 190 andfiber bundle 198 are centered within housing 202, thus creating auniform clearance space 208 within housing 202.

In FIG. 29, a first potting tool 210, comprising a first potting toolend 212, a first potting tool sleeve 214, and a slender potting toolarbor 216, may be prepared for use, by assembling an entry sleeve 218all the way onto potting tool arbor 216, and attaching an arbor support220 to the tip of potting tool arbor 216. All of these just-listedcomponents may be axisymmetric.

First potting tool 210 may then be assembled onto housing 202, asillustrated in

FIG. 29. As potting tool arbor 216, entry sleeve 218, and arbor support220 pass through the center of fiber bundle 198, they may displacefilter fibers radially outward so as to form what will become centralvoid 232.

Second potting tool 222, comprising second potting tool end 224, andsecond potting tool sleeve 226, may then be assembled to housing 202. Anarbor support recess 228 in second potting tool end may receive the tipof arbor support 220, for the purpose of centering and supporting thetip of potting tool arbor 216.

Referring now to FIG. 30, a potting material 230 may be injected intofirst potting tool 210, and may fill all free space, and all fiberinterstitial space within first potting tool 210 and housing 202, to thelevel illustrated in FIG. 30. In a like manner, potting material 230 maybe injected into second potting tool 222. The viscosity of the pottingmaterial 230, as it is injected, may be chosen such that the materialenters the open fiber lumens only to a minimal distance. When pottingmaterial 230 is fully cured, first potting tool 210 and second pottingtool 222 may be removed.

Referring now to FIG. 31, excess potting material 230, excess fiberbundle 198, a portion of inlet sleeve 218, and a portion of arborsupport 220 may be cut back so that the surfaces of the remainingportions of the fibers and potting are flush with housing ends 204 ofhousing 202. This process re-exposes the lumens of the fibers in fiberbundle 198. Potting tool arbor 216, entry sleeve 218, and arbor support220 displaced filter fibers radially outward, when they were inserted.Cured potting material 230 has now rendered the ends of fiber bundle 198immobile, such that when potting tool arbor was removed, a central void232 was left in fiber bundle 198.

The filter assemblage of FIG. 31 is now completed, ready for end caps tobe added.

An inlet cap 234, having a blood inlet 236, an inlet tube 238, and adialysate inlet 240 is assembled to housing 202, with inlet tube 238inserted into inlet sleeve 214. Inlet cap 234 is bonded to housing 202at inlet cap-housing joint 242. A seal may be established at inlettube-entry sleeve joint 244 by adhesive bonding or by other suitablemeans.

An outlet cap 246, having a dialysate outlet 248, may be bonded tohousing 202 at outlet cap-housing joint 250.

An outlet sleeve 256, having a blood outlet 252, may be positioned overoutlet cap 246 and housing flange 254, and may be bonded along outletsleeve-tube flange joint 262, and outlet sleeve-outlet cap joint 264.

A plurality of housing outlet ports 258, through the wall of housing202, may connect outer clearance/collection space 208, of FIG. 28, tooutlet channel 260, thence to blood outlet 252.

The completed cartridge is illustrated in FIG. 32.

In use, this fourth embodiment of an improved cartridge for dialysis orultrafiltration receives a dialysate solution through dialysate inlet240, and the dialysate solution then passes down through the lumens ofthe fibers of fiber bundle 198, and out through dialysate outlet 248.Blood from a patient is introduced through blood inlet 236, then flowsthrough inlet tube 238 and inlet sleeve 218, into central void 232. Fromcentral void 232, blood flows more or less uniformly radially outwardthrough the interstitial space in fiber bundle 198, passing throughaxial filter screen 190, into clearance space 208, then moving downwardin clearance/collection space 208 to pass radially outward throughhousing outlet ports 258, into outlet channel 260. Blood then movescircumferentially in outlet channel 260 to blood outlet 252.

Further Comments

Although the various embodiments of the invention have been described inconnection with blood flowing in the inter fiber space, it would also bepossible to use embodiments of the invention in a more conventionalsystem configuration in which blood flows in the fiber lumens anddialysate flows in the inter fiber space. Such an arrangement couldachieve more uniform distribution of dialysate in the inter fiber spacethan is achieved in the prior art. Such improved dialysate flowdistribution could have benefit in improving the magnitude andconsistency of clearance provided by such dialyzers. It is known, inconventional hemodialysis, that nonuniform distribution of dialysateflowing in the inter fiber space does occur and can make the cartridgeless efficient than would be the case for a more uniform flowdistribution.

It is possible that design of embodiments of the invention could befurther optimized by Computational Fluid Dynamics or by experimentationor by a combination of both methods. In general a goal of any suchoptimization can be to provide flow in the inter fiber space that issubstantially uniform and has either no stagnation points or stagnationpoints that are as few and as small as possible.

The various embodiments of the invention could be used for dialysis orrelated therapy or generally for any therapy or modality. Void flowchannels could be used with any type of orbital distributor, even if thegeometry is not as illustrated in the first embodiment. Embodiments ofthe invention could be used for purposes other than the describedcartridges that were intended for processing bodily fluids.

The ports of the cartridge could comprise Luer lock connectors for portsthat are intended to handle blood, and could comprise Hansen styleconnectors for ports that are intended to handle dialysate, regardlessof which compartment of the cartridge that is.

All cited references are incorporated by reference herein in theirentirety. Features described herein may be combined in any combination.Steps of a method may be performed in any order that is physicallypossible. Although embodiments of the invention have been describedherein, it is desired that the scope be limited only by the scope of thefollowing claims.

We claim:
 1. A cartridge for processing a fluid, said cartridgecomprising: a housing that is generally tubular, having a housing wall,a first end, an opposite second end, and having a midplane locatedmidway between the first end and the opposite second end; and aplurality of fibers, at least some of said plurality of fibers beinghollow and having porous walls or a semipermeable membrane, at leastportions of said fibers being contained within said housing, saidplurality of fibers being potted near their ends in a potting material,wherein said plurality of fibers are arranged as a bundle of fibers thatare generally parallel to each other at least at said midplane of saidhousing, and wherein at said midplane of said housing, said plurality offibers are substantially uniformly distributed throughout an interiorregion of said housing and said plurality of fibers in said bundle offibers having an average fiber-centerline-to-fiber-centerline spacing,wherein, adjacent to said potting material, said bundle of fiberscontains at least one void flow channel that is substantially open andhas a transverse dimension that is at least 3 times said averagefiber-centerline-to-fiber-centerline spacing, wherein said void flowchannel adjoins an outer circumference of said fiber bundle and extendsinwardly to a radially more inward location.
 2. The cartridge of claim1, further comprising a distributor that is in fluid communication withsaid void flow channel.
 3. The cartridge of claim 1, wherein saidhousing comprises a passageway through said housing wall, saidpassageway being in fluid communication with said void flow channel. 4.The cartridge of claim 1, wherein at said midplane of said cartridge,said fibers are distributed substantially uniformly across across-section of said housing taken perpendicular to a longitudinaldirection of said housing.
 5. The cartridge of claim 1, wherein saidcartridge has a plurality of said void flow channels at said end of saidcartridge, and said void flow channels are distributed equiangularlyaround a circumference of said fiber bundle.
 6. The cartridge of claim1, wherein said void flow channel extends radially inward more than halfof a radial dimension of said fiber bundle measured at said pottingmaterial, but does not extend entirely to a central axis of said fiberbundle.
 7. The cartridge of claim 1, wherein said void flow channel istapered in a radial direction, being wider near an outer circumferenceof said fiber bundle and narrower closer to a longitudinal axis of saidfiber bundle.
 8. The cartridge of claim 1, wherein said void flowchannel is tapered in an axial direction, being wider near said pottingmaterial and narrower closer to said midplane.
 9. The cartridge of claim1, wherein said housing is internally tapered near said first end. 10.The cartridge of claim 1, further comprising a radial channel in saidpotting material, wherein said radial channel in said potting materialadjoins said void flow channel in said fiber bundle.
 11. The cartridgeof claim 1, wherein said plurality of fibers has a central porositythrough said plurality of fibers near a midplane of said cartridge, andhas a transitional porosity through said plurality of fibers furtheraway from said midplane toward an end, and has an end porosity throughsaid plurality of fibers adjacent to said potting material, and whereinsaid end porosity through said plurality of fibers is greater than saidtransitional porosity through said plurality of fibers, and saidtransitional porosity through said plurality of fibers is greater thansaid central porosity through said plurality of fibers.
 12. Thecartridge of claim 1, wherein a first quantity is defined as a totalcross-sectional area of a fiber region excluding said void flow channelsminus a total cross-sectional area of said fibers, and a second quantityis defined as a total cross-sectional area of said fiber regionexcluding said void flow channels, and an end porosity is defined atsaid cartridge as said first quantity divided by said second quantity,and wherein said end porosity at said end of said cartridge is greaterthan a similarly defined porosity anywhere else in said fiber bundlebetween said end and said midplane of said cartridge.
 13. A systemcomprising the cartridge of claim 1, wherein said system is constructedto flow blood past exterior surfaces of said plurality of fibers andflow dialysate through lumens of said plurality of fibers.
 14. A systemcomprising the cartridge claim 1, wherein said system is constructed toflow blood through lumens of said plurality of fibers and flow dialysatepast exterior surfaces of said plurality of fibers.
 15. A cartridge forprocessing a fluid, said cartridge comprising: a housing; a plurality offibers, at least some of said plurality of fibers being hollow andhaving porous walls or a semipermeable membrane, at least portions ofsaid plurality of fibers being contained within said housing, saidplurality of fibers having an average fiber-to-fiber spacing at amid-region of said cartridge, and said plurality of fibers beingsubstantially uniformly distributed at said mid-region of saidcartridge; a first barrier, wherein said plurality of fibers, at a firstend, are potted in said first barrier, said first barrier having aninwardly-facing surface facing toward said mid-region of said cartridge,wherein, on said inwardly-facing surface of said barrier, on a sizescale calculated on a basis of a region that is at least three timessaid average fiber-to-fiber spacing, said plurality of fibers aredistributed non-uniformly such that at least one surface void of saidsize scale on said barrier surface is potted and devoid of fibersforming a surface void, and in some other places on said barrier surfacesaid fibers are distributed substantially uniformly on said size scale.16. The cartridge of claim 15, wherein said surface void has anelongated shape, said elongated shape extending to an outercircumference of said first barrier.
 17. The cartridge of claim 15,wherein said surface void is tapered in a radial direction, being widernear an outer circumference of said cartridge and narrower closer to alongitudinal axis of said cartridge.
 18. The cartridge of claim 15,wherein said cartridge comprises a plurality of said surface voids, saidsurface voids being equiangularly distributed with respect to a centralaxis of said cartridge.
 19. The cartridge of claim 15, wherein saidcartridge comprises a plurality of said surface voids, wherein saidsurface voids comprise two different sizes of said surface voids.
 20. Acartridge for processing a fluid, said cartridge comprising: a housing;a plurality of fibers, at least some of said plurality of fibers beinghollow and having porous walls or a semipermeable membrane, at leastportions of said plurality of fibers being contained within saidhousing, said plurality of fibers having an average fiber-to-fiberspacing at a mid-region of said cartridge, and said plurality of fibersbeing substantially uniformly distributed at said mid-region of saidcartridge; a first barrier, wherein said plurality of fibers, at a firstend, are potted in said first barrier, said first barrier having anoutwardly-facing surface facing away from said mid-region of saidcartridge, wherein, on said outwardly-facing surface of said firstbarrier, on a size scale calculated on a basis of a region that is atleast three times said average fiber-to-fiber spacing, said plurality offibers are distributed non-uniformly such that at least one surface voidof said size scale on said barrier surface is potted and devoid offibers, and in some other places on said barrier surface said fibers aredistributed substantially uniformly on said size scale.
 21. Thecartridge of claim 1, further comprising an orbital distributor, saidorbital distributor being in fluid communication with a passagewaythrough said housing wall, said orbital distributor extending entirelyaround a circumference of said housing and being in fluid communicationwith said void flow channel.
 22. The cartridge of claim 1, wherein saidplurality of fibers comprise a fiber first end and a fiber second end,and said fiber first end and said fiber second end are open to flow offluid therethrough.
 23. The cartridge of claim 15, wherein saidplurality of fibers comprise a fiber first end and a fiber second end,and said fiber first end and said fiber second end are open to flow offluid therethrough.
 24. The cartridge of claim 20, wherein saidplurality of fibers comprise a fiber first end and a fiber second end,and said fiber first end and said fiber second end are open to flow offluid therethrough.
 25. A cartridge for processing a fluid, saidcartridge comprising: a housing that is generally tubular, having ahousing wall, a first end, an opposite second end, and having a midplanelocated midway between the first end and the opposite second end; and aplurality of fibers, at least some of said plurality of fibers beinghollow and having porous walls or a semipermeable membrane, at leastportions of said fibers being contained within said housing, saidplurality of fibers being potted near their ends in a potting material,wherein said plurality of fibers are arranged as a bundle of fibers thatare generally parallel to each other at least at said midplane of saidhousing, and wherein at said midplane of said housing, said plurality offibers are substantially uniformly distributed throughout an interiorregion of said housing and said plurality of fibers in said bundle offibers having an average fiber-centerline-to-fiber-centerline spacing,and wherein, in a cross-section of said bundle of fibers in an unpottedlocation adjacent to said potting material, said cross-section containsfibers that are nonuniformly distributed within said cross-section andhave between some of said fibers an empty space having a transversedimension that is at least 3 times said averagefiber-centerline-to-fiber-centerline.
 26. The cartridge of claim 25,wherein said plurality of fibers comprise a fiber first end and a fibersecond end, and said fiber first end and said fiber second end are opento flow of fluid therethrough.